The accelerating loss of biodiversity and increasing rate of species extinction is a major threat to ecosystems around the globe. And yet, quantifying those losses at a large scale hasn t been possible, in large part due to a lack of the required infrastructure. But a new study shows that a major source for such information already exists in the form of environmental DNA (eDNA), which has been inadvertently collected in filters by thousands of ambient air quality monitoring stations in countries around the world for decades.